Iran has arrested four people suspected of trying to sabotage one of its nuclear plants, the head of its Atomic Energy Organisation said.
Ali Akbar Salehi, said officials had monitored and then arrested a "number of saboteurs" before they could carry out their plan.
"Some time ago, we uncovered sabotage activities by several people at a nuclear plant," he said in comments carried by the Mehr news agency on Sunday.
"We let them continue their activities so that we could gather more intelligence.
"We arrested them at the appropriate moment and their interrogation is ongoing."
Salehi did not identify which nuclear site they were planning to damage or when those detained were arrested.
Israel, widely believed to be the region's only nuclear-armed state, sees Iran's atomic work as a military threat and has said it will attack Iran's nuclear sites if it does not end its programme. Iran says its nuclear work is purely peaceful.
Iran accuses Israel and Western nations of being behind the assassination of Iranian nuclear scientists and of trying to damage its programme in other ways, such as by cyber attacks.